Communication systems are known to comprise a plurality of communication nodes that are coupled together via a TDM bus. A communication node may be a portable radio or mobile radio coupled to a fixed end via a wireless TDM bus. The communication node may also be components within the fixed end coupled together via a wireline TDM bus. For example, these communication nodes may be base interface modules, a controller, operator mux interface, etc.
As is known, the TDM bus comprises a plurality of successive frames, wherein each frame is time divided into a predetermined number of time slots. Typically, the first time slot is used for frame synchronization, and the last slot in the frame is dedicated to data transmission. The remaining slots are used for carrying digitized audio. Of the slots that are carrying audio, each is assigned to a communication node. Once the assignments are made and the frame pattern determined, the frame pattern remains fixed, i.e., slots carrying audio only carry audio, slots carrying data only carry data, etc.
While fixed frame patterns work well in most instances, the system may become bogged down when several communication nodes have data to transmit. As is known, each communication node transmits its data to the system via the data time slot. Once a communication node has access to the data time slot, it does not relinquish the time slot until it transmits all its data. Thus, many communication nodes could experience a significant delay before it transmits its data. However, the fixed pattern of the TDM was necessary to allow the other nodes to know when audio was being transmitted and when data was being transmitted.
Therefore, a need exists for a data transfer protocol that allows any slot within a time division multiplex bus to carry both digitized audio and data.